Antennas in a spacecraft are used to telemeter information on spacecraft operation to a ground station. Although external antennas can be used in outer space, only antennas integral with the skin of the spacecraft are usable during launch and re-entry. It then becomes a problem of some technical difficulty to design efficient antennas for useful frequencies which are light and not protruding from the spacecraft.
U.S. Pat. No. 3,172,112 to Seeley discloses a dumbell-loaded folded slot antenna. U.S. Pat. No. 3,346,865 to Jones discloses a simple slot antenna built into a dielectric radome. U.S. Pat. No. 3,518,685 to Jones discloses a dielectric-loaded simple cavity antenna in a ballistic projectile. U.S. Pat. No. 3,987,453 to Lopez discloses a balanced exciter for a wideband antenna element. U.S. Pat. No 4,197,545 to Favaloro et al discloses a stripline slot antenna adapted for use on aircraft or other vehicles. U.S. Pat. No. 4,367,475 to Schiavone discloses a linearly polarized radiating slot antenna. U.S. Pat. No. 4,373,162 to Peterson discloses a low frequency electronically steerable cylindrical slot array radar antenna. U.S. Pat. No. 4,460,894 to Robin et al discloses a laterally isolated microstrip antenna. U.S. Pat. No. Re. 29,296 to Krutsinger et al discloses a dual slot microstrip antenna device. All of the above relate the same general area of technology, and all are different because choices of frequencies, size of the vehicle and environmental conditions make unique problems requiring different solutions.
A discrete antenna of a given size may have a beamwidth that results in less than optimal coverage in a two antenna system on a cylindrical groundplane. Also a cavity antenna has an aperture that is too large to fit into a gap 2 inches wide.
A slot type antenna requires a ground plane of certain minimal size to radiate effectively. The minimum size required is an inverse function of frequency, making it difficult to accommodate the required ground plane in low frequency antennas. A slot antenna operating at ultra-high frequencies (UHF) would usually require a conducting ground plane 9 inches on either side of the slot.